The present invention generally relates to exposure, and particularly relates to: a mask employed in the manufacturing of various types of devices including semiconductor chips such as ICs, LSIs, and so forth, display devices such as liquid crystal panels and so forth, detecting devices such as magnetic heads and so forth, image-taking devices such as CCDs and so forth, micro-mechanics, the manufacturing method of the mask; and an exposure method. Here, micro-mechanics means a machine system in the order of microns having advanced features and techniques to manufacture such a system, applying semiconductor integrated circuit manufacturing techniques to the manufacturing of fine structures.
In the event of manufacturing a device using photolithography techniques, projection exposure apparatuses for projecting a pattern drawn on a mask (rectile) onto a wafer using a projection optical system and transferring the pattern, have been conventionally employed.
Mask patterns include adjacent and periodic line-and-space patterns, adjacent and periodic (that is, arrayed with the same interval as with hole diameters) rows of contact holes, isolated contact holes, other isolated patterns, and so forth. In order to transfer patterns with high resolution, there is the need to select the most appropriate exposure conditions (illumination conditions, exposure dose, and so forth) according to the type of employed patterns.
The resolution R of a projection exposure apparatus is obtained by the following Rayleigh's expression, using wavelength λ of light source and numerical aperture NA of a projection optical system.R=k1(λ/NA)Wherein k1 denotes a constant specified by a developing process or the like, and is around 0.5 and 0.7 in the case of normal exposure. From a different point of view, this expression indicates that the pattern size to be resolved can be standardized by (λ/NA) and converted by k1.
Miniaturization of patterns to be transferred, that is, increased resolution, has been increasingly required so as to respond to highly integrated devices in recent years. In order to obtain high resolution, it is effective to increase the numerical aperture NA in the Expression and to reduce the wavelength λ, however, such improvements have reached the limit as for now, so it is difficult to form a pattern below 0.15 μm on a wafer with normal exposure.
Accordingly, improvement of masks as a means for improving imaging characteristics of projection exposure apparatuses has been proposed. For example, there is a halftone mask for improving depth of focus as to an isolated contact hole. The halftone mask is a mask for attenuating light intensity on a portion corresponding to a light-shielding portion of a binary mask, and also keeping a phase difference of 180° as to a light-transmitting portion.
Alternatively, there is a phase shift mask for markedly improving resolution. The phase shift mask is a mask designed to have mutually constant phase differences in the event of incident light toward the mask passing through a light-transmitting portion In general, this phase difference is designed to be 180°. Various kinds of phase shift masks have been proposed, and approximately a half-line width can be realized as to binary masks, depending on the kind of the phase shift mask. This can be achieved by maintaining the mutual phase difference of adjacent light at 180° and mutually counteracting the amplitude of the center portions thereof.
As described above, various proposals have been made in order to form fine patterns, however, it is still extremely difficult to form fine contact hole patterns. Nowadays, the formation of fine contact hole patterns close to the resolution limit has been being studied using binary masks or halftone masks instead of phase shift masks, which are difficult to manufacture and inspect.
The present inventors and others have succeeded in exposing fine contact hole patterns onto a member being exposed, such as a wafer or the like, by disposing a supplementary pattern around the desired pattern of a binary mask and performing special oblique illumination. The supplementary pattern holes are smaller than those of the desired pattern to the extent that resolution is not affected (see the specification in USP Application Laid-Open No. 2002/0177048, for example).
However, arraying of the most appropriate supplementary pattern as to the desired pattern varies depending on the hole diameter and the pitch of the desired pattern, plus, an arraying method for the most appropriate supplementary pattern as to the desired pattern has not been fully known. Accordingly, exposure with the most appropriate supplementary pattern has not been able to be performed, leading to the problem that high resolution could not be obtained in all cases.
Alternatively, it is possible to obtain an array of the most appropriate supplementary pattern by actually performing exposure while changing. the array of the supplementary pattern, however, this takes great amounts of time, resulting in increased developing costs.